Background Worker Pattern

代码
  1using System;
  2using System.Threading;
  3using System.ComponentModel;
  4using System.Text;
  5
  6public class PiCalculator
  7{
  8    public static BackgroundWorker calculationWorker = new BackgroundWorker();
  9    public static AutoResetEvent resetEvent = new AutoResetEvent(false);
 10
 11    public static void Main()
 12    {
 13        int digitCount;
 14
 15        Console.Write("Enter the number of digits to calculate:");
 16
 17        if (int.TryParse(Console.ReadLine(), out digitCount))
 18        {
 19            Console.WriteLine("ENTER to cancel");
 20            // C# 2.0 Syntax for registering delegates
 21            calculationWorker.DoWork += CalculatePi;
 22            // Register the ProgressChanged callback           
 23            calculationWorker.ProgressChanged +=
 24                 UpdateDisplayWithMoreDigits;
 25            calculationWorker.WorkerReportsProgress = true;
 26            // Register a callback for when the                
 27            // calculation completes                           
 28            calculationWorker.RunWorkerCompleted +=
 29                   new RunWorkerCompletedEventHandler(Complete);
 30            calculationWorker.WorkerSupportsCancellation = true;
 31
 32            // Begin calculating pi for up to digitCount digits
 33            calculationWorker.RunWorkerAsync(digitCount);
 34
 35            Console.ReadLine();
 36            // If cancel is called after the calculation       
 37            // has completed it doesn't matter.                
 38            calculationWorker.CancelAsync();
 39            // Wait for Complete() to run.                     
 40            resetEvent.WaitOne();
 41        }
 42        else
 43        {
 44            Console.WriteLine(
 45                    "The value entered is an invalid integer.");
 46        }
 47    }
 48
 49    private static void CalculatePi(object sender, DoWorkEventArgs eventArgs)
 50    {
 51        int digits = (int)eventArgs.Argument;
 52
 53        StringBuilder pi = new StringBuilder("3.", digits + 2);
 54        calculationWorker.ReportProgress(0, pi.ToString());
 55
 56        // Calculate rest of pi, if required
 57        if (digits > 0)
 58        {
 59            for (int i = 0; i < digits; i += 9)
 60            {
 61
 62
 63                // Calculate next i decimal places
 64                int nextDigit = PiDigitCalculator.StartingAt(
 65                      i + 1);
 66                int digitCount = Math.Min(digits - i, 9);
 67                string ds = string.Format("{0:D9}", nextDigit);
 68                pi.Append(ds.Substring(0, digitCount));
 69
 70                // Show current progress
 71                calculationWorker.ReportProgress(
 72                       0, ds.Substring(0, digitCount));
 73
 74                // Check for cancellation
 75                if (calculationWorker.CancellationPending)
 76                {
 77                    // Need to set Cancel if you need to
 78                    // distinguish how a worker thread completed
 79                    // i.e., by checking
 80                    // RunWorkerCompletedEventArgs.Cancelled
 81                    eventArgs.Cancel = true;
 82                    break;
 83                }
 84            }
 85        }
 86        eventArgs.Result = pi.ToString();
 87    }
 88
 89    private static void UpdateDisplayWithMoreDigits(object sender, ProgressChangedEventArgs eventArgs)
 90    {
 91        string digits = (string)eventArgs.UserState;
 92
 93        Console.Write(digits);
 94
 95    }
 96
 97    static void Complete(object sender, RunWorkerCompletedEventArgs eventArgs)
 98    {
 99        Console.WriteLine();
100        if (eventArgs.Cancelled)
101        {
102            Console.WriteLine("Cancelled");
103        }
104        else if (eventArgs.Error != null)
105        {
106            // IMPORTANT: check error to retrieve any exceptions.     
107            Console.WriteLine(
108                "ERROR: {0}", eventArgs.Error.Message);
109        }
110        else
111        {
112            Console.WriteLine("Finished");
113        }
114        resetEvent.Set();
115
116    }
117}
118
119public class PiDigitCalculator
120{
121    // 
122    public static int StartingAt(int i)
123    {
124        Thread.Sleep(1000);
125        return i;
126    }
127}